1. Field of the Invention
The present invention relates to a compact well jack, and more particularly to a pump jack of the counter balance type which is particularly adapted to reciprocating a long stroke rod pump.
2. Description of the Prior Art
With depleting oil reserves in the U.S., it is becoming more and more common to produce wells by pumping. The industry widely uses pumping systems including a downhole reciprocating pump having a plunger which is raised and lowered by a sucker rod string connected at the surface end of the well with a walking beam. This system is often referred to as a "rod pump". The rod pump is commonly reciprocated by a walking beam which is generally driven by pitman arms connected with crank arms rotated by a shaft which is driven by an electric motor or an internal combustion engine, commonly using natural gas or liquified petroleum gas as fuel. The motor or engine is coupled with the shaft through belts, chains, and some form of transmission. Counter weights are generally mounted on the crank arms. The center of the walking beam is pivoted on a samson post at a sufficient height to permit the beam to rocked by the pitman arms for raising and lowering the sucker rod string in the well.
The conventional walking beam type pumping jack or unit, though very widely used, is not a particularly efficient system having many bearings and other parts which are subject to wear. It is also often quite large and expensive when used on deep wells. For example, such a pump having a stroke of twenty feet may be forty feet high. Obviously, such a pump will have a large, long walking beam and quite heavy counter weights. Some deep wells have even been known to use pumps having an eighty foot stroke. The massive components of such a pumping system must be moved during the operation of the pump causing substantial wear in the many bearings, gears, and other elements in the drive system and require time consuming and expensive maintenance
Even with the foregoing disadvantages, the conventional
beam pump jack is looked upon by the industry as being "tried and true" and is not likely to be widely displaced for most shallow artificial lift operations. It does, however, have two serious disadvantages in specialized situations where improved pumping systems are needed.
On offshore platforms, where space is very limited, depletion of reserves leads to the need for artificial lift, and most offshore platforms simply do not have the room needed or the load bearing capacity available to install banks of huge walking beam pump jacks.
In very deep wells, use of a very long stroke is particularly advantageous because of the elastic effect of the long strings of sucker rod. With a walking beam pump, it is necessary to go to a truly massive piece of equipment to get the length of stroke needed.
The two foregoing disadvantages of conventional walking beam are addressed by U.S. Pat. No. 4,651,582 which seems to be the closest approach to the invention of this application found in a limited search of prior U.S. patents.
There, however, remains a need in the industry for improved pump jacks, particularly for deep well operations and for use on offshore platforms.